1. Field of the Invention
The present invention relates generally to alternators and in particular to a permanent magnet alternator whose output voltage can be mechanically regulated by varying the exposure of the alternator windings to a magnetic flux field.
2. Description of the Related Art
Permanent magnet alternators are utilized for conversion of mechanical energy into electrical energy. In one typical design, the basic alternator includes a permanent magnet rotor. Magnets are arranged within the rotor to create a magnetic flux field. This flux field is defined by the number of magnets used and the spatial arrangement of magnets. A stator is disposed within the rotor adjacent the magnets. The stator contains a plurality of conductive coils, or windings, which are exposed to the magnetic flux field created by the rotor. When this flux field changes, i.e., when the magnets are moved relative to the coils, an electromotive force (EMF) is induced in the coils, creating an electrical current. The current is then supplied to various electrical and auxiliary systems, such as voltage regulators, storage devices (i.e. batteries), electrical loads, and so forth. In vehicles, such alternators are often used in conjunction with an internal combustion engine for generating electrical power needed for operation.
Typical operation of a permanent magnet alternator involves rotating the rotor relative to the stator to create a continuously rotating magnetic flux field as seen by the stator. Exposure to the rotating flux field generates current through the coils. Rotation of the rotor is accomplished by application of mechanical force to the rotor. The applied force is usually supplied by a rotating shaft, concentrically coupled to the rotor. The rotor may thus be associated with a rotating member, such as a flywheel. The shaft may be the output shaft of an internal combustion engine, or it may be an independent shaft connected to gears or a series of belts and pulleys. However, regardless of the means of connection utilized, in an engine application the shaft and rotor are typically tied, in some form, to an output shaft of the internal combustion engine. Thus, when the engine speed increases, rotational speed of the rotor increases proportionally.
In such an arrangement as described above, the electrical output from the alternator is tied directly to engine speed. However, the electrical requirements, such as current and voltage, of any given system may vary at levels different from the engine speed. For example, the electrical supply requirements for an electrical system may increase exponentially in comparison to the speed of the engine. Thus, since the speed of the alternator is directly tied to the speed of the engine, the actual electrical output will not always match the electrical requirements of a given system, or these requirements may vary substantially during operation. One such example is an electronic fuel injector. As engine speed increases a fuel injector must deliver fuel at an increased rate. The fuel injector experiences an increase in load, and thus also has increased electrical requirements. It may become desirable in this example to supply electrical current at a rate greater than that which is typically available for the given engine speed if the two were to increase and decrease proportionally.
The opposite of the above example may also be at issue. An electrical system may have electrical supply requirements that remain constant independent of the engine speed. In this case, the electrical output of a typical alternator will equal the supply requirements of the system only at one particular engine speed. At all other engine speeds the electrical output will be either greater or less than that which is required by the electrical system.
Various electrical componentry is often utilized to control the output of a permanent magnet alternator. In particular, voltage regulators may be employed to condition generated power to conform to electrical system requirements. This componentry can, however, be quite costly as compared to other system circuits. Accordingly, there is a need for alternative schemes for regulating output of an alternator, particularly in internal combustion engine applications.
The present invention is directed to overcoming, or at lest reducing the affects of, one or more of the problems set forth above.